Method for producing insulated gate thin film semiconductor device

ABSTRACT

An amorphous semiconductor film is etched so that a width of a narrowest portion thereof is 100 μm or less, thereby forming island semiconductor regions. By irradiating an intense light such as a laser into the island semiconductor regions, photo-annealing is performed to crystallize it. Then, of end portions (peripheral portions) of the island semiconductor regions, at least a portion used to form a channel of a thin film transistor (TFT), or a portion that a gate electrode crosses is etched, so that a region that the distortion is accumulated is removed. By using such semiconductor regions, a TFT is produced.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention disclosed in the specification relates to amethod for producing a semiconductor device having a gate electrodeusing a crystalline thin film semiconductor, for example, a thin filmtransistor (TFT). As application of the TFT, an active matrix typeliquid crystal display device has been known. This display deviceperforms a fine and high resolution display by arranging a TFT as aswitching element in each of several hundred thousands or more pixelsdisposed at a matrix form.

[0003] 2. Description of the Related Art

[0004] Recently, a transistor using a thin film semiconductor formed ona glass or quartz substrate, such as a thin film transistor (TFT) hasbeen concerned. A thin film semiconductor having a thickness of several100 to several 1000 Å is formed on a surface of a glass substrate or aquarts substrate, and then the transistor (insulated gate field effecttransistor) is formed using the thin film semiconductor.

[0005] Of such the TFT, a TFT using an amorphous silicon film and a TFTusing a crystalline silicon film is used in practice. Since the TFTusing the crystalline silicon film has a superior characteristic, it hasa great future.

[0006] In the TFT using a crystalline silicon semiconductor, thecrystalline silicon thin film is obtained by a method forthermal-annealing an amorphous silicon film, or a method for forming acrystalline silicon film directly using a vapor phase growth method.However, in order to perform the process at a low temperature, aphoto-annealing for crystallizing an amorphous silicon film byirradiating an intense light such as a laser has been proposed. (forexample, Japanese Patent Application Open No. 4-37144)

[0007] There are two methods roughly as a case wherein crystallinesilicon film is obtained by photo-annealing includes. In a first method,photo-annealing is performed after etching a semiconductor thin filminto a shape of an element to be formed. In a second method, afterphoto-annealing for an even (flat) film is performed, the film is etchedinto a shape of an element to be formed. In general, it has known thatthe element obtained by the first method has a superior characteristic(field effect mobility) than that obtained by the second method. Thismay be because in the first method, the film is contracted byphoto-annealing, and thus a central portion of a pattern is stressed,thereby increasing crystallinity of the film.

[0008] However, there is a problem in this case. That is, although aninitial characteristic is good, by use for a long period of time, thecharacteristic is deteriorated largely.

[0009] A cause that the characteristic is deteriorated by theconventional method will be explained with FIGS. 3A to 3D. Initially, anisland semiconductor region 31 of amorphous silicon having a rectangle32 is formed as shown in FIG. 3A. When photo-annealing is performed, thefilm is contracted slightly by crystallization. A dot line of the figurerepresents a size of the island semiconductor region before thephoto-annealing. In this contract process, a region 33 that distortionis accumulated in an outermost portion of the island semiconductorregion 31 is formed. The crystallinity of such the region 33 is not highso much. (FIG. 3B)

[0010] In a case wherein a gate electrode 34 is formed across such theisland region (FIG. 3C), in an (a-b) cross section (FIG. 3D) along thegate electrode, the region 33 that distortion is accumulated is to beformed under the gate electrode 34 and a gate insulating film 35. When avoltage is applied to the gate electrode 34, since an interfacecharacteristic between the region 35 and the gate insulating film is notgood, charges are trapped, so that deterioration occurs by a parasiticchannel or the like due to the charges. (FIG. 3D)

SUMMARY OF THE INVENTION

[0011] The object of the present invention is to prevent such thedeterioration, and to provide a method for producing an insulated gatesemiconductor device having less deterioration.

[0012] According to a first aspect of the present invention, thefollowing processes are obtained.

[0013] (1) An amorphous semiconductor film is etched into a first shapethat a width of a narrowest portion is 100 μm or less, to form an islandsemiconductor region.

[0014] (2) The semiconductor region is photo-annealed to crystalize itor to increase the crystallinity thereof.

[0015] (3) Of end portions (or peripheral portions) of the semiconductorregion, at least a gate electrode or a channel forming region of asemiconductor device is etched by 10 μm or more from ends, to form asemiconductor region having a second shape.

[0016] Also, according to a second aspect of the present invention, thefollowing processes are obtained.

[0017] (1) An amorphous semiconductor film is etched into a first shapethat a width of a narrowest portion is 100 μm or less, to form an islandsemiconductor region.

[0018] (2) The semiconductor region is photo-annealed to crystalize itor to increase the crystallinity thereof.

[0019] (3) At least a part of end portions (or peripheral portions) ofthe semiconductor region is etched.

[0020] (4) An gate insulating film is formed to cover the semiconductorregion.

[0021] (5) An gate electrode is formed across the etched portion of theend portions of the semiconductor region.

[0022] (6) An N-type or P-type impurity is introduced or diffused usingthe gate electrode as a mask.

[0023] In the first and second aspects of the present invention, thefirst shape is one of a rectangle, a regular polygon and an ellipse(including a circle), and generally it is preferred that a shape doesnot include a concave portion at any point on a periphery.

[0024] In the above structure, an amorphous silicon film is formed on asubstrate having an insulating surface, such as a glass substrate or aquartz substrate by plasma chemical vapor deposition (plasma CVD) andlow pressure thermal CVD. In photo-annealing, various excimer laserssuch as a KrF excimer laser (wavelength of 248 nm) and a XeCl excimerlaser (wavelength of 308 nm), and a Nd:YAG laser (wavelength of 1064 nm)and a second harmonic component (wavelength of 532 nm) and a thirdharmonic component (wavelength of 355 nm) may be used. In the presentinvention, a light source may pulse-oscillate or continuous-oscillate.As disclosed in Japanese Patent Application Open No. 6-318701, inphoto-annealing, crystallization may be promoted using a metal element(for example, Fe, Co, Ni, Pd or Pt) which promotes crystallization ofsilicon.

[0025] The present invention disclosed in the specification is effectivein a case wherein an island semiconductor region is constructed in asingle-crystalline region or a region equivalent to thesingle-crystalline region. As described later, the single-crystallineregion or the region equivalent to the single-crystalline region can beobtained by scan-irradiating a linearly processed laser light into anamorphous silicon film and a crystalline silicon film.

[0026] The single-crystalline region or the region equivalent to thesingle-crystalline region is defined as a region that the followingconditions are satisfied.

[0027] (1) The region does not contain substantially crystal boundary.

[0028] (2) The region contains hydrogen or a halogen element toneutralize a point defect at a concentration of 1×10¹⁵ to 1×10²⁰ atomscm⁻³.

[0029] (3) The region contains carbon or nitrogen at a concentration of1×10¹⁶ to 5×10¹⁸ atoms cm⁻³.

[0030] (4) The region contains oxygen at a concentration of1×10¹⁷ to5×10¹⁹ atoms cm⁻³.

[0031] The above concentrations are defined as a minimum value of ameasurement value measured by secondary ion mass spectrometry (SIMS).

[0032] In the present invention disclosed in the specification, only achannel portion is etched so as not to be adjacent to a channel thatinfluences characteristics of a semiconductor device. This correspondsto that etching is performed so as not to remain such a region in aportion which crosses a gate electrode.

[0033]FIGS. 1A to 1D show a basic structure of the present invention. Aplurality of island amorphous semiconductor regions 11 (four regions inthe figures) are formed into a rectangle 12 having a long side (a) and ashort side (B) as a first shape. In the present invention, it isrequired that a width of the narrowest portion of the first shape is 100μm or less. This is because, when the width is 100 μm or more, an effectfor characteristic improvement due to contraction of a film atphoto-annealing is not obtained. Thus (b) is 100 μm or less in length.(FIG. 1A)

[0034] Next, photo-annealing is performed. Thus, the islandsemiconductor regions are crystallized and contracted at the same time.A dot line of the figure represents a size of the island semiconductorregions before the photo-annealing. New peripheries of the islandregions are represented by numeral 14. Regions 13 that distortion isaccumulated due to distortion process can be formed in peripheralportions of the island semiconductor regions.; (FIG. 1B)

[0035] Then, the peripheral portions of the island semiconductor regions11 is etched to form a semiconductor region 15 for the formation ofnecessary elements (FIG. 1C), and an gate insulating film (not shown)and a gate electrode 16 are formed. (FIG. 1D)

[0036] When it is not necessary that all the regions 13 that distortionis accumulated is removed, a method as shout in FIGS. 2A to 2D can beused. In this method, an amorphous semiconductor region 21 having arectangle 22 is formed (FIG. 2A), and then photo-annealed. As a result,as shown in FIGS. 1A to 1D, the semiconductor region 21 is contracted,so that a region 23 that distortion is accumulated is formed in aperipheral portion. (FIG. 2B)

[0037] A region including a peripheral portion of a region that a gateelectrode is formed is etched (FIG. 2C), and than a gate insulating film(not shown) and a gate electrode 26 are formed. Since the region 23 thatdistortion is accumulated is not included in a channel 25 formed underthe gate electrode 26, as similar to a case of FIGS. 1A to 1D,deterioration can be decreased (FIG. 2D)

[0038] In the present invention, it is preferred that an amorphoussemiconductor region at photo-annealing has a possible simple shape withrespect to the first shape, for example, a rectangle, a regular polygonand an ellipse including a circle. When, as shown in FIG. 4A, asemiconductor region 41 having a shape 42 that a central portion isconcave is photo-annealed, since a concave portion 44 of the centralportion is pulled in upper and lower directions (for a source and adrain, for example) a: contraction of a film, crack or the likegenerates easily in this region. (FIGS. 4B and 4C)

[0039] This is because, as shown in FIG. 4C (an arrow represents acontraction direction), contraction of a film occurs from a widestportion. Thus, it is desired that the first shape is not a shape havinga concave portion, but is a shape having a convex portion in the wholeregion or a shape not having a concave portion in the whole region.

[0040] Therefore, even if the rectangle as shown in FIGS. 1A to 1D isused as the first shape, it is not preferred that a ratio between thelong side (a) and the short side (b) is very large. It is preferred thata/b≦10.

[0041] Also, when an island semiconductor region is constructed as aregion equivalent to a single-crystalline region or a regionsubstantially equivalent to the single-crystalline region, atcrystallization distortion is accumulated in a peripheral portion of theisland semiconductor region.

[0042] Since this distortion concentrates in the peripheral portion ofthe island semiconductor region, influence by this distortion can besuppressed by removing a portion around the island semiconductor region.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043]FIGS. 1A to 1D show schematic producing processes (upper views) ofthe present invention;

[0044]FIGS. 2A to 2D show schematic producing processes (upper views) ofthe present invention;

[0045]FIGS. 3A to 3D show schematic conventional producing processes(upper and cross section views);

[0046]FIGS. 4A to 4 c are views explaining a stress applied to a thinfilm semiconductor at photo-annealing;

[0047]FIGS. 5A to 5F show producing processes in Embodiment 1;

[0048]FIGS. 6A to 6G show producing processes in Embodiment 2;

[0049]FIGS. 7A to 7E and 8A to 8C show producing processes in Embodiment3;

[0050]FIGS. 9 and 10 are upper views representing a state that a linearlaser light is irradiated into an active layer (island semiconductorregion; and

[0051]FIG. 11 is an upper view representing a crystallization state whena linear laser light is irradiated into an active layer (islandsemiconductor region).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] Embodiment 1

[0053] The embodiment is described with FIGS. 5A to 5F. In FIGS. 5A to5F, cross sections of two thin film transistors (TFTs) is shown. A leftis a cross section obtained by cutting a TET in vertical to a gateelectrode thereof (in vertical to a-b in FIG. 3C), and a right is across section obtained by cutting a TFT in parallel with a gateelectrode thereof (along a-b in FIG. 3C). An upper view is referred withFIG. 1D.

[0054] A silicon oxide film 502 having a thickness of 3000 Å is formedas a base film on a glass substrate 501 by sputtering or plasma chemicalvapor deposition (plasma CVD). Also, By plasma CVD or low pressurethermal CVD, an amorphous silicon film 503 having a thickness of 500 Åis formed. Phosphorus is doped into the amorphous silicon film 503 toform N-type impurity region 504 and 505 which become a source and adrain in a TFT. (FIG. 5A)

[0055] The amorphous silicon film 503 is etched to form island siliconregions 506 and 507. (FIG. 5B)

[0056] A KrF excimer laser light is irradiated to crystallize a siliconfilm. At this irradiation the regions 504 and 505 into which thephosphorus is introduced are crystallized and activated at the sametime. A energy density of the laser is preferably 150 to 500 mJ/cm². Thelaser irradiation process may include two steps or more using laserlights at different energy.

[0057] In the embodiment, after a laser light having an energy densityof 250 mJ/cm² is irradiated two to ten pulses, a laser light having anenergy density of 400 mJ/cm² is irradiated two to ten pulses. Asubstrate temperature at laser irradiation is set to 200° C. A suitableenergy density of the laser depends on a substrate temperature and afilm duality of the amorphous silicon film 503.

[0058] As a result, regions 508 that distortion is accumulated areformed in end portions (peripheral portions) of the island siliconregions 506 and 507. (FIG. 5C)

[0059] End portions 509 of the island silicon regions 506 and 507 areetched to form new island silicon regions 510 and 511. Portions etchedby this process are shown by dot lines 509. (FIG. 5D)

[0060] By plasma CVD, a silicon oxide film 512 (gate insulating film)having a thickness of 1200 Å is formed. Also, an aluminum film(containing 0.3% scandium (Sc)) having a thickness of 5000 Å isdeposited on the film 512 by sputtering and then etched to form gateelectrodes 513 and 514. (FIG. 5E)

[0061] By plasma CVD, a silicon oxide film 515 (interlayer insulatorhaving a thickness of 5000 Å is deposited, and then contact holes areformed in the film 515. By sputtering, an aluminum film having athickness of 5000 Å is deposited and etched to form electrode-wirings516 and 517 for a source and a drain. (FIG. 5F)

[0062] By the above processes, a TFT is produced. To obtain a stablecharacteristic, it is preferred that annealing is performed at one(atmospheric) pressure in an atmosphere containing hydrogen (250 to 350°C.) after a contact hole forming process.

[0063] Embodiment 2

[0064] The embodiment is described with FIGS. 6A to 6G. As similar toFIGS. 5A to 5F, In FIGS. 6A to 6G, cross sections of two thin filmtransistors (TFTs) is shown. A left is a cross section obtained bycutting a TFT in vertical to a gate electrode thereof, and a right is across section obtained by cutting a TFT in parallel with a gateelectrode thereof. An upper view is referred with FIG. 2D.

[0065] A silicon oxide film 602 having a thickness of 3000 Å is formedas a base film on a glass substrate 601 by sputtering or plasma CVD.Also, By plasma CVD or low pressure thermal CVD, an amorphous siliconfilm 603 having a thickness of 500 Å is formed. An aqueous solutioncontaining nickel acetate (or cobalt acetate) at 1 to 100 ppm is appliedto a surface of the film 603 to form a nickel acetate (cobalt acetate)layer 604. Since the nickel acetate (cobalt acetate) layer 604 isextremely thin, it is not always in a film form. (FIG. 6A) Thermalannealing is performed at 350 to 450° C. for 2 hours in an atmospherecontaining nitrogen, to decompose nickel acetate (cobalt acetate) anddiffuse nickel (or cobalt) into the amorphous silicon film 603 at thesame time. Then, the amorphous silicon film 603 is etched to from islandsilicon regions 605 and 606. (FIG. 6B) A KrF excimer laser light isirradiated to crystallize a silicon film by photo-annealing. In theembodiment, after a laser light having an energy density of 200 mJ/cm²is irradiated two to ten pulses, a laser light having an energy densityof 350 mJ/cm² is irradiated two to ten pulses. A substrate temperatureat laser irradiation is set to 200° C.

[0066] A suitable energy density of the laser depends on a concentrationof the applied nickel (cobalt) in addition to a substrate temperatureand a film quality of the amorphous silicon film. In the embodiment, ithas confirmed that a concentration of nickel (cobalt) contained in theamorphous silicon film is 1×10¹⁵ to 5×10¹⁶ atoms/cm³ from the analysisresult by secondary ion mass spectrometry (SIMS).

[0067] A method for performing photo-annealing using a catalytic elementwhich promotes crystallization is disclosed in Japanese patentApplication Open No. 6-318701.

[0068] As a result, regions 607 that distortion is accumulated areformed in end portions (peripheral portions) of the island siliconregions 605 and 606. (FIG. 6C)

[0069] In end portions 607 of the island silicon regions 605 and 606,only portions which cross a gate electrode are etched to form new islandsilicon regions. The portions etched by this process are shown by dotlines 608. (FIG. 6D)

[0070] By plasma CVD, a silicon oxide film 609 (gate insulating film)having a thickness of 1200 Å is formed. Also, a poly-crystalline siliconfilm (containing 1% phosphorus) having a thickness of 5000 Å isdeposited on the film 609 by low pressure CVD and then etched to formgate electrodes 610 and 611. (FIG. 6E)

[0071] By ion doping, an phosphorus ion is introduced into a siliconfilm using the gate electrode as a mask. A doping gas is phosphine (PH₃)diluted with hydrogen at 5%. An accelerating voltage is preferably 60 to110 kV. A dose is 1×10¹⁴ to 5×10¹⁵ atoms/cm². Thus, N-type impurityregions (source and drain) 612 and 613 are formed.

[0072] After the doping, thermal annealing is performed at 450° C. for 4hours, Thus, the impurity can be activated. This is because nickel(cobalt) is contained in a semiconductor region. (See Japanese PatentApplication Open No. 6-267989)

[0073] After the thermal annealing process for activation,photo-annealing may be performed by irradiating a laser light or thelike.

[0074] After the above process, annealing is performed at oneatmospheric pressure in an atmosphere containing hydrogen (250 to 350°C.), to neutralize dangling bonds in an interface between a gateinsulating film and a semiconductor region. (FIG. 6F)

[0075] By plasma CVD, a silicon oxide film 616 (interlayer insulatorhaving a thickness of 5000 Å is deposited, and then contact holes areformed in the film 616. By sputtering, an aluminum film having athickness of 5000 Å is deposited and etched to form electrode-wirings614 and 615 for a source and a drain. (FIG. 6G)

[0076] Embodiment 3

[0077] In the embodiment, a metal element which promotes crystallizationof silicon is introduced into an amorphous silicon film and then a laserlight is irradiated to form a region substantially equivalent to asingle-crystalline region, so that an active layer of a TFT isconstructed using the region substantially equivalent to thesingle-crystalline region.

[0078]FIGS. 7A to 7E show a part of producing processes of a TFTaccording to the embodiment. A silicon oxide film 702 having a thicknessof 3000 Å is formed as a base film on a glass substrate 701 by plasmaCVD or sputtering. Also, an amorphous silicon film 703 having athickness of 500 Å is formed by plasma CVD or low pressure thermal CVD.

[0079] A sample formed on the substrate is placed on a spinner 700. Inthis state, a nickel acetate solution having an adjusted nickelconcentration is applied to the sample to form an aqueous (water) film704. This state is shown in FIG. 7A. By spin dry using the spinner 700,an unnecessary nickel acetate solution is removed (blown away). Thus, astate that a small amount of nickel is held in contact with the surfaceof the amorphous silicon film is obtained.

[0080] By patterning, an active layer 705 of a TFT is formed. At thisstate, the active layer 705 is constructed by the amorphous silicon film703. (FIG. 7B)

[0081] In this state, a laser light is irradiated to crystalize theactive layer 705 made of the amorphous silicon film 703. The used laserlight is processed into a linear beam. The laser light is irradiatedfrom one side of the active layer 705 to an opposite side thereof whilescanning the linear laser light. It is necessary to use apulse-oscillated excimer laser as a laser light. In the embodiment, aKrF excimer laser (wavelength of 248 nm) is used.

[0082] The laser light is irradiated while a substrate is heated at 500°C. This is because of the relaxation of large change of a crystalstructure due to laser light irradiation. It is preferred that theheating temperature is 450° C. to a temperature equal to and lower thanthe distortion point of a glass substrate.

[0083] When the linear laser light is irradiated into the amorphoussilicon film, a region into which the laser light is irradiated ismelted instantaneously. By irradiating the linear laser light whilescanning it, crystal growth progresses gradually. Thus, the regionequivalent to the single-crystalline region can be obtained.

[0084] That is, as shown in FIG. 7C, in a case wherein a linear laserlight 708 is irradiated gradually from one end portion of the activelayer 705 constructed by the amorphous silicon film 703 to the otherportion thereof while scanning it, a region 707 equivalent to thesingle-crystalline region is crystal-grown in accordance with the laserlight irradiation, the whole active layer 705 can be obtained at asingle-crystalline equivalent state.

[0085] Thus, an active layer 709 constructed by a silicon thin filmequivalent to a single-crystalline thin film is obtained. (FIG. 7D)

[0086] The region equivalent to the single-crystalline region isrequired to satisfy the following conditions.

[0087] (1) The region does not contain substantially crystal boundary.

[0088] (2) The region contains hydrogen or a halogen element toneutralize a point defect at a concentration of 1×10¹⁵ to 1×10²⁰ atomscm⁻³.

[0089] (3) The region contains carbon or nitrogen at a concentration of1×10¹⁶ to 5×10¹⁹ atoms cm⁻³.

[0090] (4) The region contains oxygen at a concentration of 1×10¹⁷ to5×10¹⁹ atoms cm⁻³.

[0091] In a case wherein the metal element which promotescrystallization of silicon, as described in the embodiments is used, itis necessary to contain the metal element at a concentration of 1×10¹⁶to 5×10¹⁹ cm⁻³ in a film. If the metal element is contained at aconcentration larger than the concentration range, a semiconductorcharacteristic is not obtained but a metallic characteristic isobtained. Also. if the metal element is contained at a concentrationlower than the concentration range, an action for promotingcrystallization of silicon cannot be obtained.

[0092] From the above description, the silicon film region which isobtained by the laser light irradiation and is equivalent to thesingle-crystalline region is essentially different from a commonlycalled single-crystal such as a single-crystalline wafer.

[0093] At crystallization by the laser light irradiation, contraction ofa film occurs, and the distortion is accumulated largely towardperipheral portions of the active layer 709. That is, the distortion isconcentrated in a portion 710 as shown in FIG. 7D and accumulated.

[0094] In general, a thickness of the active layer is about severalhundreds Å to several thousands Å. A size thereof is several μm squareto several hundreds μm square. That is, it is extremely thin and has athin film form. In such a thin film form state, if crystal growth asshown in FIG. 7C progresses, the distortion is concentrated in aperipheral portion, i.e., a portion around a region that crystal growthis completed or a region that crystal growth does not progress any more.

[0095] From the above two causes, the distortion is concentrated aroundthe active layer. It is not preferred that a region in which suchdistortion is concentrated is present in the active layer 709 since theregion may influence the operation of a TFT.

[0096] Thus, in the embodiment, the whole peripheral portion of theactive layer 709 is etched, As a result, an active layer 711 which isconstructed by the region substantially equivalent to thesingle-crystalline region and in which influence due to stress isreduced can be obtained. (FIG. 7E) After the active layer 711 isobtained, as shown in FIG. 8A, a silicon oxide film having a thicknessof 1000 Å is formed as a gate insulating film 712 by plasma CVD, tocover the active layer 111. A poly-crystalline silicon film into which alarge amount of phosphorus (P) is doped is formed at a thickness of 5000Å by low pressure thermal CVD and then patterned to from a gateelectrode 713. (FIG. 8A)

[0097] An phosphorus (F) ion is implanted by plasma doping or ionimplantation, to form a source region 714 and a drain region 716 in aself-alignment. Also, by using the gate electrode 713 as a mask, aregion 715 into which an impurity ion (phosphorus) is not implanted isdetermined as a channel forming region. (FIG. 8B)

[0098] A silicon oxide film 717 having a thickness of 7000 Å is formedas an interlayer insulating film by plasma CVD using a tetraethoxysilane(TEOS) gas. After forming contact holes, source and drain electrodes 718and 719 are formed using a multilayer film of titanium and aluminum.Although not shown in figures, a contact electrode for the gateelectrode 713 is formed at the same time. Then, heating treatment isperformed at 350° C. for 1 hour in an atmosphere containing hydrogen, tocomplete a TFT as shown in FIG. 8C.

[0099] Since the obtained TFT is constructed by a silicon film of whichthe active layer is equivalent to single-crystal, an electricalcharacteristic of the obtained TFT can be almost equal to that of a TFTwhich is produced using an SOI technique or the like and constructedusing a single-crystalline silicon film.

[0100] Embodiment 4

[0101] In the embodiment, a manner for irradiating a laser light into anamorphous silicon film patterned to construct an active layer ismodified in the structure of Embodiment 3, in order to crystallize iteasily.

[0102]FIG. 9 shows a method for irradiating a laser light into an activelayer in the processes according to Embodiment 3. In this method, alinear laser light having a longitudinal direction is irradiated inparallel with one side of a patterned amorphous silicon film 901 (sincethis film becomes an active layer later, it is called the active layer).By scanning along a direction of an arrow while irradiating the laserlight, the active layer 901 is converted into the region equivalent to asingle-crystalline region.

[0103] In the method according to the embodiment, a scan direction ofthe linear laser light 900 can be set so as to progress crystal growthform a corner portion of the active layer 901, as shown in FIG. 10. Whenthe laser light irradiation method of FIG. 10 is used, since crystalgrowth progresses gradually from a narrow region toward a wide region,as shown in FIG. 11, the progress of crystal growth is performed easily.In comparison with a case wherein the laser light is irradiated in thestate as shown in FIG. 9, the region equivalent to thesingle-crystalline region can be formed and high repeatability can beobtained.

[0104] According to the present invention, deterioration of an insulatedgate type semiconductor device produced using a semiconductor devicecrystallized by photo-annealing can be decreased. Although, n theembodiments, a silicon semiconductor is mainly described, the sameeffect is also obtained in another semiconductor such as asilicon-germanium alloy semiconductor, a zinc sulfide semiconductor anda silicon carbide semiconductor. Thus, the present invention has anindustrial value.

What is claimed is:
 1. A method for forming a semiconductor devicecomprising: forming a semiconductor film comprising silicon over asubstrate; and irradiating said semiconductor film with a linear laserlight to form a region to become at least a channel formation region insaid semiconductor film, wherein said region to become at least achannel formation region contains hydrogen at a concentration of 1×10¹⁵to 1×10²⁰ atoms cm⁻³, also contains carbon and nitrogen at aconcentration of 1×10¹⁶ to 5×10¹⁸ atoms cm⁻³, and further containsoxygen at a concentration of 1×10¹⁷ to 5×10¹⁹ atoms cm⁻³.
 2. A methodfor forming a semiconductor device comprising: forming a semiconductorfilm comprising silicon over a substrate; and irradiating saidsemiconductor film with a linear laser light to form a region to becomeat least a channel formation region in said semiconductor film, whereinsaid region to become at least a channel formation region containshydrogen and halogen at a concentration of 1×10¹⁵ to 1×10²⁰ atoms cm⁻³,also contains carbon and nitrogen at a concentration of 1×10¹⁶ to 5×10¹⁸atoms cm⁻³, and further contains oxygen at a concentration of 1×10¹⁷ to5×10¹⁹ atoms cm⁻³.
 3. A method for forming a semiconductor devicecomprising: forming a semiconductor film comprising silicon over asubstrate; and irradiating said semiconductor film with a linear laserlight to form a single-crystalline region or region equivalent to thesingle-crystalline region to become at least a channel formation regionin said semiconductor film, wherein said single-crystalline region orregion equivalent to the single-crystalline region containssubstantially no crystal boundary therein, contains hydrogen at aconcentration of 1×10¹⁵ to 1×10²⁰ atoms cm⁻³, also contains carbon andnitrogen at a concentration of 1×10¹⁶ to 5×10¹⁸ atoms cm⁻³, and furthercontains oxygen at a concentration of 1×10¹⁷ to 5×10¹⁹ atoms cm⁻³.
 4. Amethod for forming a semiconductor device comprising: forming asemiconductor film comprising silicon over a substrate; and irradiatingsaid semiconductor film with a linear laser light to form asingle-crystalline region or region equivalent to the single-crystallineregion to become at least a channel formation region in saidsemiconductor film, wherein said single-crystalline region or regionequivalent to the single-crystalline region contains substantially nocrystal boundary therein, contains hydrogen and halogen at aconcentration of 1×10¹⁵ to 1×10²⁰ atoms cm⁻³, also contains carbon andnitrogen at a concentration of 1×10¹⁶ to 5×10¹⁸ atoms cm⁻³, and furthercontains oxygen at a concentration of 1×10¹⁷ to 5×10¹⁹ atoms cm⁻³.
 5. Amethod for forming a semiconductor device comprising: forming anamorphous semiconductor film comprising silicon over a substrate;forming an amorphous semiconductor island comprising silicon by etchingsaid amorphous semiconductor film into a first shape having a narrowestwidth of 100 μm or less; irradiating said semiconductor island with alinear laser light to form a single-crystalline region or regionequivalent to the single-crystalline region to become at least a channelformation region in said semiconductor island; and etching an endportion of said semiconductor island to narrow a portion of saidsemiconductor island from said end portion of said semiconductor islandby 10 μm or more to form a second shape semiconductor region which hasthe narrowed portion in at least said channel formation region, whereinsaid single-crystalline region or region equivalent to thesingle-crystalline region contains substantially no crystal boundarytherein, contains hydrogen and halogen at a concentration of 1×10¹⁵ to1×10²⁰ atoms cm⁻³, also contains carbon and nitrogen at a concentrationof 1×10¹⁶ to 5×10¹⁸ atoms cm⁻³, and further contains oxygen at aconcentration of 1×10¹⁷ to 5×10¹⁹ atoms cm⁻³.
 6. A method according toclaim 1 wherein said linear laser light is a laser light selected fromthe group consisting of a KrF excimer laser light, a XeCl excimer laserlight, a Nd:YAG laser light, a second harmonic of said Nd:YAG laserlight and a third harmonic of said Nd:YAG laser light.
 7. A methodaccording to claim 1 wherein said substrate is selected from the groupconsisting of a glass substrate and a quartz substrate.
 8. A methodaccording to claim 2 wherein said linear laser light is a laser lightselected from the group consisting of a KrF excimer laser light, a XeClexcimer laser light, a Nd:YAG laser light, a second harmonic of saidNd:YAG laser light and a third harmonic of said Nd:YAG laser light.
 9. Amethod according to claim 2 wherein said substrate is selected from thegroup consisting of a glass substrate and a quartz substrate.
 10. Amethod according to claim 3 wherein said linear laser light is a laserlight selected from the group consisting of a KrF excimer laser light, aXeCl excimer laser light, a Nd:YAG laser light, a second harmonic ofsaid Nd:YAG laser light and a third harmonic of said Nd:YAG laser light.11. A method according to claim 3 wherein said substrate is selectedfrom the group consisting of a glass substrate and a quartz substrate.12. A method according to claim 4 wherein said linear laser light is alaser light selected from the group consisting of a KrF excimer laserlight, a XeCl excimer laser light, a Nd:YAG laser light, a secondharmonic of said Nd:YAG laser light and a third harmonic of said Nd:YAGlaser light.
 13. A method according to claim 4 wherein said substrate isselected from the group consisting of a glass substrate and a quartzsubstrate.
 14. A method according to claim 5 wherein said linear laserlight is a laser light selected from the group consisting of a KrFexcimer laser light, a XeCl excimer laser light, a Nd:YAG laser light, asecond harmonic of said Nd:YAG laser light and a third harmonic of saidNd:YAG laser light.
 15. A method according to claim 5 wherein saidsubstrate is selected from the group consisting of a glass substrate anda quartz substrate.
 16. A method according to claim 1 wherein saidsemiconductor device is a liquid crystal display.
 17. A method accordingto claim 2 wherein said semiconductor device is a liquid crystaldisplay.
 18. A method according to claim 3 wherein said semiconductordevice is a liquid crystal display.
 19. A method according to claim 4wherein said semiconductor device is a liquid crystal display.
 20. Amethod according to claim 5 wherein said semiconductor device is aliquid crystal display.